Clamping tools in which a clamping bolt is slidably mounted in a housing are known in the art. A locking piston is also slidably movable in the housing preferably at right angles to the clamping bolt. The position of the clamping bolt is accomplished by the cooperation of wedging inclines. One wedging incline is provided on the locking piston or rather on its piston rod, while the other wedging incline is provided on an inner end of the clamping bolt.
These clamping tools must make sure that the workpiece is securely held in place on a surface in such a way that during a machining operation the forces effective on the workpiece do not diminish or remove the clamping force.
European Patent Publication EP 0,620,084 and corresponding German Patent Laying-Open Publication 43 11 857 disclose a clamping tool for clamping workpieces by a clamping head that is slidingly guided on an inclined plane in such a way that the frictional forces between the plane and the clamping head are larger than the forces effective on the clamping head. The inclined plane is formed between a lower section of the clamping head that is formed into a pestle and the piston rod of a clamping force holding element extending crosswise to the force direction of the clamping head. In order to increase the frictional force in the area of the inclined plane a V-groove is formed in the wedging incline of the piston rod and the pestle is formed with wedging bevels sliding in the V-groove. In order to move the clamping head against the workpiece two hydraulic drives are required, one for the clamping head and one for the holding piston. The need for separate hydraulic drives results in a relatively large structural assembly. U.S. Pat. No. 5,746,420 (Kohlbert) discloses a similar device as just described.
U.S. Pat. No. 5,915,679 (Kohlert) discloses a support element for securing a workpiece on a supporting surface, for example in a machine tool. The support element comprises a support or holding bolt movably mounted in a housing. The bolt is moved into contact with a workpiece by an air stream. Once contact is established, the holding bolt is held in place by a hydraulic piston extending in the same housing at right angles to the holding bolt. When the hydraulic locking piston is released, the holding bolt is reset into a rest position by a spring. The workpiece is contacted under a manual throttle control of the air stream and firmly held in place by hydraulic pressure. Here again two sources of pressure, one hydraulic one pneumatic are required for the operation of the clamping tool.
There is a trend in the technology of clamping tools to make these tools ever smaller while maintaining their high efficiency in a structurally compact component.